Surface impoundment
Surface impoundment means a unit that is a natural topographical depression, man-made excavation, or diked area formed primarily of earthen materials (although it may be lined with man-made materials), which is designed to hold an accumulation of liquids. Examples of surface impoundments include holding, storage, settling, and aeration pits, ponds, and lagoons.
Source
40 CFR § 63.681
Scoping language
All terms used in this subpart shall have the meaning given to them in this section, 40 CFR 63.2 of this part, and the Act.